MUSINA, South Africa (AP) -- It's easy to miss the two girls. They are so small they seem to disappear amid the dozen Zimbabwean boys crowded around them along the trash-choked drain. Sofia Chimhangwa, a 14-year-old in a denim skirt, lies on the concrete under a filthy blanket. Her 15-year-old friend sits next to her, braiding a legless Barbie's hair. Sofia says she survives because the other girl's 19-year-old boyfriend helps feed them both when the coins they beg don't stretch far enough. "We shouldn't be here on our own. I know that,'' Sofia said. Her big sister helped her get to the border from Zimbabwe's capital Harare. After eight months in this border town, Sofia is not ready to go home because she cannot yet take money back to her widowed father. She is among an increasing number of young Zimbabweans setting out on their own to escape their homeland's economic ruin, bringing both a child's naive sense of invincibility and a grown-up desire to help their families. International aid group Save the Children says some 500 Zimbabwean youngsters are in Musina today, compared to about 50 five years ago. But those committed to helping these children are increasingly anguished over one question: Where are the girls? Aid workers say they don't see enough Sofias -- teenage girls -- to account for the number that men, women and boys say they accompanied across the border. Some disappear as maids or "wives'' into homes around this dusty mining town split by railroad tracks. On one side of the tracks are the crowded "locations'' where blacks were forced to live under apartheid; on the other are the neighborhoods of broad roads and large houses still predominantly inhabited by whites. Other girls hang back in the shadows at Musina's truck stops at night along with older prostitutes. There are fears traffickers are recruiting girls into the sex trade in Johannesburg, some 500 kilometers (300 miles) south, and other South African cities. As the representative in Musina of Lawyers for Human Rights, Sabelo Sibanda tries to ensure Zimbabweans aren't illegally detained or deported before they can apply for refugee status. But he's grown wary of pushing too hard for the release of young girls from a government deportation center here, at least until he can be sure into whose hands they will fall. He said he found a home with Zimbabwean relatives living in South Africa for two girls he met at the center who had crossed the border to look for jobs as waitresses in Cape Town. One was 13, Sibanda said, adding "the other said she was about 20, but I don't believe that.'' He was less successful with another pair, 18- and 16-year-olds who said they were raped on both sides of the border crossing into South Africa. Sibanda found them a place at a shelter for abused women. He said the older girl later told him that while on a walk in town, they were approached by men offering them food and clothes. The girls returned to the shelter after an older woman warned them not to listen. "A few days later, the younger one went to town, and just never came back,'' Sibanda said. "The level of vulnerability for girls and young women is very, very high,'' he said. "There's so many of them, and they're so desperate. They'll just jump at anything.'' In the year or so he has headed the Musina office of the International Organization for Migration, Mohamed Hassan has helped scores of Zimbabwean boys return home. But he said only a few girls came to him for help. Hassan got a sense of how many more girls there were when the South African government opened an office at a fair ground to process Zimbabweans seeking asylum. A makeshift refugee camp grew up on a sandy lot across the street, and unaccompanied girls were suddenly visible, making up perhaps 25 percent of all the teens on their own. "They would come for documentation, and that would be the last time anyone would see them,'' he said. Conditions in the refugee camp turned so bad -- there were reports of rape and offers to pay for sex -- that the South African government shut the place down. "It was just some sort of fishing ground for those with ill intentions,'' Hassan said. An International Organization for Migration study last year found established routes used by human traffickers in South Africa, bringing girls and young women from the countryside into the cities to work as prostitutes or maids. But the victims rarely come forward. Some may not even think of themselves as victims because they were aware the jobs being offered were in the sex trade. Others may be too ashamed, or too thankful just to have work, to speak out. Forster Kwangwari, a Zimbabwean preacher who ran a shelter for street children in his homeland before opening one here last year, says the refugee girls in Musina are vulnerable. "People can easily take them, to be domestic workers, to be wives,'' Kwangwari said. "Men adopt them before we see them. They see them before we see them.'' The ragged young Zimbabweans on Musina's streets know Kwangwari well, judging by the cries of "Pastor! Pastor!'' following him along the main street. He offers steady meals, a chance to go to school and to play, but he's persuaded only 20 boys to come to his shelter, a shed-like building furnished with foam mattresses. Kwangwari said children living on the streets quickly come to value their independence above everything. He's set aside rooms for girls but does not get enough donations to afford the separate staff he would need to look after them. Two other shelters in town cater largely to boys, as few girls come forward. A girl who gave her name as Tracy said she had thought she was doing fine on her own. Then, one evening, the 16-year-old was mugged, raped and shot through the neck. After leaving the hospital -- two scars still pink on either side of her neck -- she made her way to a shelter and was looking for help to go home. Tracy had left her widowed father in the Masvingo region of Zimbabwe more than a year ago and found a job almost immediately. "I was just walking around, and someone said: 'Come work for me,''' she said. She was paid 400 rand (about $100) a month to clean a house, and spent 150 rand of her earnings each month to rent a room in a poor neighborhood in the shadow of two iron-gray hills created by mine tailings. She wasn't able to save much. So she's looking for more work before she heads home. "I want to buy groceries to take to my father,'' she said. Musina is "not a good place,'' Tracy said. "There are no jobs. There's no place to stay. A lot of robbery. Girls are forcing themselves into prostitution to get money. And others are forcing themselves into temporary marriage, to stay with boyfriends for security.'' However, she said she would not discourage any young Zimbabwean girl from coming here, adding she would likely return herself one day -- a measure of the desperation in her homeland. With an economic free-fall, collapsed hospital infrastructure and deadly cholera epidemic, aid agencies are feeding most of the population in Zimbabwe. For many Zimbabweans, the only road to survival remains the one leading to South Africa. First, men left in search of work. As times got worse, women, too, had to leave. And, finally, children. In some cases, Zimbabwean parents who have established a foothold send for their children, paying transporters known as "amalaitsha'' to bring them to South Africa. Children have been abandoned, some with no idea where their parents are, by amalaitsha fleeing police or border guards. Other children have told aid workers of hopping a train to the border and then simply walking across on their own. Sibekiwe Moyo came to Musina from the Beitbridge area just across the border, blending in with a van load of neighbors heading to a football match. Her grandmother had sent her to find work. Sibekiwe, a bright, shy 14-year-old, once wanted to be a teacher. Now she says that's no longer possible "because I am no longer in school.'' She last attended classes in 2006. Money ran out for fees, then the education system collapsed. Sibekiwe's father is dead and she and her grandmother lost track of her mother and 19-year-old brother when they crossed into South Africa several years ago. Once in South Africa, Sibekiwe wandered into a housing compound for workers on a farm overlooking the Limpopo River about 40 kilometers (25 miles) from Musina. She was offered work baby-sitting, seven days a week for 200 rand (about $20) a month, plus food and a place to sleep in one of the compounds mud-walled, tin-roofed shacks. Her wages are probably a fifth of the earnings of the farm worker who pays her to watch the baby while she tends melons. The 8-month-old whom Sibekiwe had secured to her back with a pale yellow towel could be her little brother. Sibekiwe speaks Venda, as do the South Africans in this area. She points out a few other Zimbabwean girls looking after other babies. One, 14-year-old Thembi Ndlovu, has been here three months, and plans to work until December, then return to Zimbabwe for the new school year. "I'll go back to school after I've earned some money here,'' she said. Sibekiwe, who had been in South Africa only three days, had more modest goals. She hoped to one day save enough to send money to her grandmother. "I'm not big,'' she said. "But I can work and help.''